Data compression/expansion using a rice encoder/decoder

ABSTRACT

A data compression apparatus for data compressing a digital information signal obtained from a digital audio signal. The digital information signal includes p-bit samples, where p is an integer larger than 1. The apparatus has an input (16) for receiving the digital information signal, and a lossless compression unit (18) for carrying out a substantially lossless compression step on the digital information signal so as to obtain a data compressed digital information signal. The lossless compression unit includes a Rice encoder, which is distinguishable by a code parameter m. Further, an output terminal (22) is available for supplying the data compressed digital information signal. The Rice encoder has a generator unit (30) for generating the code parameter m from N samples of the digital information signal, in accordance with a formula which optimizes the value of m for each frame of N samples.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a data compression apparatus for datacompressing a digital information signal obtained from a digital audiosignal, the digital information signal comprising p-bit samples, where pis an integer larger than 1, the apparatus comprising

means for receiving the digital information signal,

lossless compression means for carrying out a substantially losslesscompression step on the digital information signal so as to obtain adata compressed digital information signal, the lossless compressionmeans comprising a Huffman type encoder,

output means for supplying the data compressed digital informationsignal, to a data expansion apparatus for data expanding a datacompressed digital information signal obtained from a digital audiosignal, the apparatus comprising

input means for receiving the data compressed digital informationsignal,

lossless expanding means for carrying out a substantially lossless dataexpansion step on the data compressed digital information signal so asto obtain a replica of the digital information signal, the losslessexpanding means comprising a Huffman type decoder,

output means for supplying the replica of the digital informationsignal, to a transmitter comprising the data compression apparatus, to areceiver comprising the data expansion apparatus, and to a method fordata compressing said digital information signal.

2. Description of the Related Art

Huffman type encoders and decoders are well known in the art. Referenceis made in this respect to the publication `A method for theconstruction of minimum-redundancy codes`, by D. A. Huffman in Proc. ofthe IRE, Vol. 40(10), September 1952, and to the publication `Adaptivevariable length coding for efficient compression of spacecrafttelevision data`, by R.F. Rice et al in IEEE Trans on CT, vol. 16(9),1971.--.

For the DVD (Digital Versatile Disc) an audio-only application calledDVD Audio is, at the time of writing, under discussion. If all wishesfrom the audio community with respect to the number of channels,sampling frequency, number of bits per sample and playing time have tobe accommodated, even the high capacity of DVD is not sufficient.

SUMMARY OF THE INVENTION

The invention aims at providing a data compression apparatus and a dataexpansion apparatus which is very suitable for data compressing andexpanding a digital audio signal.

The data compression apparatus in accordance with the invention ischaracterized in that the Huffman type encoder is a Rice encoder, whichRice encoder is distinguishable by a code parameter m, the Rice encodercomprising generator means for generating said code parameter from Nsamples of the digital information signal in accordance with thefollowing formula: ##EQU1## where A and B are constants and x[n] is then-th sample of the N samples, where N is an integer larger than 0.Further, a data expansion apparatus for data expanding a data compresseddigital information signal obtained from a digital audio signal, theapparatus comprising

input means for receiving the data compressed digital informationsignal,

lossless expanding means for carrying out a substantially lossless dataexpansion step on the data compressed digital information signal so asto obtain a replica of the digital information signal, the losslessexpanding means comprising a Huffman type decoder,

output means for supplying the replica of the digital information signalis characterized in that the Huffman type decoder is a Rice decoder,which Rice decoder is distinguishable by a code parameter m, the Ricedecoder comprising generator means for generating said code parameterfrom N samples of the replica of the digital information signal inaccordance with the following formula: ##EQU2## where A and B areconstants and x[n] is the n-th sample of the N samples, where N is aninteger larger than 0. The invention is based on the followingrecognition.

A number of different formats have been proposed for DVD Audio, allclaiming to fulfill requirements set by consumers, content providers,equipment manufacturers, etc. Most proposals are enhancements of thecurrent CD parameters: higher sampling rate, increased resolution, andmore channels. The common constraints for all of the proposed DVD Audioformats are a playing time of at least that of the current CD Audio,which is approximately 75 minutes and the fact that lossy compression isnot acceptable for high quality audio. Another requirement formulated isthat to suit both the people with two-channel stereo reproductionequipment and those with 5-channel reproduction equipment, both atwo-channel and a multi-channel signal should be available. Since, ingeneral, these two mixes are created in a studio out of a high number ofchannels, the stereo signal is not necessarily a down-mix of themultichannel signal. Therefore, matrixing is not an option forretrieving the 2-channel mix from the 5-channel mix. Thus, in total2+5=7 separate channels are required.

In order to store these signals on a DVD, while leaving sufficientplaying time, the bit rate needs to be reduced.

Lossless coding can provide the bit-rate reduction needed withoutcompromising audio quality in any way. An important requirement set isthat editability should be possible on DVD. This means that the losslessdecoder should be able to start decoding at any position on a predefinedgrid, i.e. without the need for decoding previous data. Finally thedecoder should be of low complexity since it will be present in everyDVD player.

A lossless audio coding scheme will be proposed which is able to realisethe required compression ratio, eg. for DVD Audio.

Lossless coding is a technique to reduce the required storage capacityfor data, such as text files and computer program data. After decoding,the compressed data is perfectly reconstructed. Well known text and datacompression programmes and techniques such as "Lempel Ziv", "pkzip","compress" and "pack" result in a relatively poor compression ratio whenapplied on a PCM audio signal.

The specific characteristic of a PCM audio signal is that audio isrepresented as a sequence of PCM (multi-bit) samples, which makes itmore effective to process the PCM samples instead of the individual bitsor bytes. Between consecutive PCM samples dependencies exist. Theirexploitation in enhanced lossless audio coding algorithms result in ahigher compression ratio.

Generally, a lossless audio coder can be broken up into two basicoperations, `source modelling` by means of prediction and entropycoding.

Source modelling is applied to the audio signal so as to obtain aresidual of the audio signal, suitable for encoding in an Entropyencoder. The residual signal is data compressed by means of entropycoding. This results in a variable-rate bit stream which is transmittedover the channel. The bit stream also contains source model parametersand other side information.

In the decoder the original input signal is reconstructed by entropydecoding and source synthesis.

The objective of the encoder is to optimize data compression, so as torealize a maximum data compression ratio. The challenge at the decoderside is to minimize the complexity.

In one embodiment of the invention, the short term (pseudo) stationarityof signals is exploited in the data compression step, by analyzing andprocessing the signal in frames. This period of pseudo stationarity isin the order of 25 ms. The advantage of processing a signal in frames isthat these frames can be seen as isolated blocks providing editability.In practice, the statistical properties of an audio signal vary and thusalso the optimal frame length varies. However, for an easy handling, theframe length is chosen constant.

The frame length can, as an example, be set at 1024 samples for 44.1 kHzsampling frequency, corresponding to 23 ms. This appears to be a goodbalance between editability and performance. For shorter frame lengthsthe compression performance decreases and for longer frame lengths theeditability becomes impractical.

In another embodiment, no framing is used, but the data compression of asample is determined by N previous samples of the information signal tobe data compressed.

Linear predictive coding, also known as intra-channel prediction, isapplied to remove the linear dependencies between successive samples ofthe audio signal. In a general linear prediction scheme, a residualsignal x[n] is constructed by subtracting a prediction of the audiosignal from the audio signal. The prediction of the current sample ofthe audio signal is based on previous samples of the audio signal.

Variable length coding, finally, removes redundancy from the signalx[n]. Again, in this whole process, no information is lost. There arenumerous methods available for entropy coding. For a low decodercomplexity, in accordance with the invention, a Huffman like code isused.

The Rice codes appeared to be a promising subset of the Huffman codes,since they can be distinguished by only one parameter m. For adescription of Rice codes, reference is made to document D2 in the listof related documents. The Rice code is in essence the Huffman code for aLaplacian probability density function (PDF) ##EQU3## which turns out tobe a good approximation for the actual residual signal x[n]. TheLaplacian PDF is matched to p(x) by only one parameter σ.

A Rice code-word obtained from a sample word of the residual signal x[n]consists of four parts. The first part is a single bit indicating thesign of the sample. The second part consists of the m least significantbits (LSBs) of the absolute value of the sample. The third part is theunary representation of sample without the m LSBs. The final part is asingle bit delimiter for the unary notation.

In the first mentioned embodiment, the value of m is optimized for eachframe of N samples by means of the following formula: ##EQU4## where Aand B are constants and x[n] is the n-th sample of the N samples, whereN is an integer larger than 0.

Preferably, A=1 and B=1 and m=.left brkt-bot.M, where ##EQU5## and thesign `.left brkt-bot.` signifies a rounding of the value of M to thevalue of the nearest lower integer.

Decoding a Rice code-word is straightforward and requires very fewcomputations. The sign bit and the m LSBs are directly available. Theremaining part can be reconstructed by simply counting the number ofzero-valued bits prior to the delimited bit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated further with reference to the embodiments described in thefollowing FIGURE description, in which

FIG. 1 shows an embodiment of the data compression apparatus,

FIG. 2 shows the probability of occurrence of the samples of a signal asa function of their amplitude, for a wideband digital audio signal andfor a residual signal obtained from said wideband digital audio signalafter prediction and subtracting the audio signal from its predictedversion,

FIG. 3 shows the data compression apparatus of FIG. 1 incorporated in arecording apparatus for recording the data compressed information signalon a record carrier,

FIG. 4 shows the data compression apparatus incorporated in atransmission apparatus for transmitting the data compressed digitalinformation signal via a transmission medium,

FIG. 5 shows a further embodiment of the recording apparatus, furtherprovided with an error correction encoder and a channel encoder,

FIG. 6 shows an embodiment of the data expansion apparatus forreconverting the data compressed digital information signal into areplica of the original information signal,

FIG. 7 shows the data expansion apparatus of FIG. 6 incorporated in areproducing apparatus for reproducing the data compressed digitalinformation signal from a record carrier, and

FIG. 8 shows the data expansion apparatus of FIG. 6 incorporated in areceiving apparatus for receiving the data compressed digitalinformation signal from a transmission medium, and

FIG. 9 shows a further embodiment of the reproducing apparatus, furtherprovided with a channel decoder and an error correction unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the data compression apparatus inaccordance with the invention. The apparatus has an input terminal 1 forreceiving p-bit samples of a digital audio signal, eg. sampled at 44.1kHz. The apparatus comprises a prediction unit 2, well known in the art,which has an input 4 coupled to the input terminal 1, and an output 6.The output 6 of the prediction unit 2 is coupled to an input 10 of asignal combination unit 10, which has a second input 12 coupled to theinput terminal 1 and an output 14. The output 14 is coupled to aterminal 16 which is the input of a data compression unit 18. An output20 of the data compression unit 18 is coupled to an output terminal 22of the apparatus.

The prediction unit 2 is adapted to generate a predicted version of thedigital audio signal applied to its input 4 and to supply the predictedversion to the output 6. The signal combination unit 10 is adapted tocombine the audio signal applied to its input 12 and the predictedversion of the audio signal applied to its input 8 in a subtractive way,so as to obtain a residual output signal which is supplied to the output14. The output signal present at the output 14 of the combination unit10 is representative of the error between the digital audio signalapplied to the input 12 and the predicted version of the audio signalapplied to the input 8. When the samples of both the digital audiosignal and the predicted version of the digital audio signal are appliedto the combination unit 10 with the same polarity, the combination unit10 will be in the form of an subtractor unit. However, if the samples ofone of the digital audio signal and the predicted version of the digitalaudio signal are inverted in polarity relative to the other one of thetwo signals, prior to combining them in the combination unit 10, thecombination unit 10 will be in the form of a adder unit.

In general, it can be said that the prediction unit 2 and thecombination unit 10 result in decreasing the variance in the amplitudedistribution of the digital audio signal. As an example, the curve 25 inFIG. 2 shows the amplitude distribution of the digital audio signalapplied to the input 1, whilst the curve 27 shows the amplitudedistribution of the residual signal present at the terminal 16.

The signal having the amplitude distribution in correspondence with thecurve 27 can be encoded very efficiently by means of a data compressionunit 18 which is of the Huffman type. More specifically, an even moreefficient encoding can be realised by means of a compression unit 18 inthe form of a Rice encoder. The Rice encoder 16 includes a datacompressor 28 and a generator unit 30 for determining a parameter m,which is supplied to in the data compressor 28 so as to enable encodingof the signal supplied to the input 16.

The functioning of the Rice encoder 18 is as follows. The parameter m isa value which is representative of the mean position of the mostsignificant `1` bit in N samples of the information signal applied tothe input 16. Suppose, the value of m equals 3, and that a 16-bit sampleof the information signal applied to the input 16 has to be encoded inthe Rice encoder. Encoding said 16-bit sample in the data compressor 28is realized by taking the (m=)3 least significant bits of the 16-bitsample. The decimal value corresponding to the remaining 13 bit wordequals the number of `zeroes` to be added to the m least significantbits, followed by a `1`-bit and a sign-bit, the sign bit indicating thepolarity of the sample.

An example: suppose the 16-bit sample has a decimal value of 19. Thissample thus equals `0000 . . . 010011`. With m=3, the bits 011 areretrieved from the sample. The remaining 13-bit word equals `0000 . . .010`, which corresponds to the decimal value 2. As a result two `zeroes`are added, followed by a `1` bit. In addition a `sign` bit is addedbefore the bit sequence obtained. The resulting data compressed sampleequals `?011001`, where the ?-sign indicates the sign-bit. As a result,the 16bit sample is compressed into a 7-bit word.

In order to data expand the data compressed sample, it is required toknow the value m, so that the value m should be transmitted as well.

It should however be noted that it is not always necessary to transmitthe value m, namely in those situations where m is derived from Nsamples preceding the sample to be compressed. This will be made clearlater on in this description.

The derivation of the value for the parameter m will be describedhereafter. The generator unit 30 receives N samples supplied to theinput 16 and derives the value for m using the following formula:##EQU6## where A and B are constants and x[n] is the n-th sample of theN samples, where N is an integer larger than 1.

More specifically, m=.left brkt-bot.M, where ##EQU7## and the sign`.left brkt-bot.` signifies a rounding of the value of M to the value ofthe nearest lower integer. It will be clear that in another embodimentone could have rounded M to the value of the nearest higher integer. Butthis would mean a lower data compression ratio realized in thecompressor 28.

In one option, the value m for encoding (data compressing) a sample canbe derived from N samples preceding the sample to be converted. In thisoption, the encoding of the first N samples require a special treatment.As an example, where N is assumed to be equal to 10, for encoding thefirst sample, m could be chosen a predetermined value, eg. equal to p,or p/2. For encoding the second sample, m could be obtained using theabove formula for N=1, using the first sample value. For encoding thethird sample, m could be obtained using the above formula for N=2, usingthe first and second sample value, and so on, until upon encoding the11th sample the above formula can be used for N=10, using the previousten sample values.

In this option, there is no need for transmitting the m values to acorresponding Rice decoder, as will be made clear hereafter, whendiscussing such Rice decoder.

In a second option, the generator unit 30 is adapted to generate thecode parameter m for subsequent frames of N samples of the digitalinformation signal, as per one of the formula given above. Thecompressor 28 encodes a frame of N samples in accordance with the mvalue derived for that frame. In this option, it is required to transmitthe value for m for each frame together with the data compressed samplesin that frame to a corresponding Rice decoder so as to enable a decodingof the data compressed information signal, in order to obtain a replicaof the original information signal.

In a preferred embodiment, A and B are both chosen equal to 1.

Encoding the information signal in the way described above offers a moresimple derivation of the parameter m, compared to prior art Riceencoders, as well as a slightly better performance than those prior artRice encoders.

FIG. 3 shows the incorporation of the data compression apparatus of FIG.1 in a recording apparatus. The recording apparatus further comprises awrite unit 35 for writing the data compressed information signal in atrack on the record carrier 32. In the present example, the recordcarrier 32 is a magnetic record carrier, so that the write unit 35comprises at least one magnetic head 34 for writing the data compressedinformation signal in the record carrier 32. The record carrier mayhowever be an optical record carrier, such as a CD disk or a DVD disk.

FIG. 4 shows an embodiment of a transmitter for transmitting an audiosignal via a transmission medium TRM, comprising the data compressionapparatus as shown in FIG. 1. The transmitter further comprises atransmission unit 40 for applying the data compressed information signalto the transmission medium TRM. The transmission unit 40 could comprisean antenna 42.

Transmission via a transmission medium, such as a radio frequency linkor a record carrier, generally requires an error correction encoding anda channel encoding carried out on the data compressed information signalto be transmitted. FIG. 5 shows such signal processing steps carried outon the residual signal for the recording arrangement of FIG. 3. Therecording arrangement of FIG. 5 therefore comprise an error correctionencoder 50, well known in the art, and a channel encoder 52, also wellknown in the art.

FIG. 6 shows an embodiment of the data expansion apparatus in accordancewith the invention. The apparatus has an input terminal 55 for receivingthe data compressed words of the data compressed information signal. Theinput terminal 55 is coupled to an input of a data expansion unit 58which is of the Huffman type. More specifically, the expansion unit 58is in the form of a Rice decoder. The Rice decoder 58 includes a dataexpander 60 and a generator unit 62 for determining a parameter m, whichis supplied to in the data expander 60 so as to enable decoding of thesignal supplied to the input 55. The Rice decoder 58 supplies a replicaof the information signal at its output 64, which output 64 is coupledto a first input 66 of a signal combination unit 68. An output of thesignal combination unit 68 is coupled to an input of a prediction unit57, well known in the art. An output of the prediction unit 57 iscoupled to the output terminal 69 as well as to a second input 67 of thecombination unit 68. The functioning of the combination unit 68 and theprediction unit 57 is well known in the art, in the sense that, inresponse to the information signal supplied to the input 66, whichinformation signal is a replica of the residual signal present at theoutput 14 of the combination unit 10 of the apparatus of FIG. 1, areplica of the original audio signal is obtained at the output terminal69.

The functioning of the Rice decoder 58 is explained hereafter. Thegenerator unit 62 is identical to the generator unit 30 in the Riceencoder of FIG. 1, and thus derives the parameter m for the decoding ofa sample in the data compressed information signal from N samples of theinformation signal previously decoded, in the same way as the generatorunit 30 in FIG. 1.

The data expansion in the data expander 60 of a data compressed sampleof the data compressed input signal supplied to the terminal 55 isrealized as follows so as to obtain a 16-bit audio sample, as in theexample given above. Use will be made of the data compressed word`?011001`, obtained above, where m was equal to 3. The data expander 60retrieves the first three bits `011` of the data compressed wordfollowing the sign bit `?`, which three bits are the three leastsignificant bits of the reconverted 16-bit sample. The two `zero` bitsin the remaining word `001` indicate that the remaining 13-bit word ofthe audio sample, after having extracted the three least significantbits, had a decimal value of 2, which results in a 13-bit word `0000 . .. 10`. The reconverted 16-bit audio sample thus equals `0000 . . .10011`, where the `?`-bit indicates the polarity of the sample.

When starting data expansion, it is not possible to derive a value for mfrom audio samples previously reconverted. So, for obtaining the firstreconverted sample from the data expander 60, m is chosen equal to apredetermined value, eg. equal to p, or p/2. For decoding(reconverting/data expanding) the second sample, m could be obtainedusing the above formula for N=1, using the first reconverted samplevalue. For decoding the third sample, m could be obtained using theabove formula for N=2, using the first and second reconverted samplevalue, and so on, until upon encoding the 11th sample the above formulacan be used for N=10, using the previous ten reconverted sample values.

In the second option, described above for the data compressionapparatus, the data expansion apparatus decodes blocks of datacompressed samples, using an m-value received from the transmissionmedium.

FIG. 7 shows the data expansion apparatus of FIG. 6 incorporated in areproduction apparatus. The reproducing apparatus further comprises aread unit 70 for reading the data compressed information signal from atrack on the record carrier 52. In the present example, the recordcarrier 32 is a magnetic record carrier, so that the read unit 70comprises at least one magnetic head 72 for reading the data compressedinformation signal from the record carrier 32. The record carrier mayhowever be an optical record carrier, such as a CD disk or a DVD disk.

FIG. 8 shows an embodiment of a receiver for receiving an audio signalvia a transmission medium TRM, comprising the data expansion apparatusas shown in FIG. 6. The receiver further comprises a receiving unit 75for receiving the data compressed signal from the transmission mediumTRM. The receiving unit 75 could comprise an antenna 77.

As has been explained above, transmission via a transmission medium,such as a radio frequency link or a record carrier, generally requiresan error correction encoding and a channel encoding carried out on thedata compressed information to be transmitted, so that a correspondingchannel decoding and error correction can be carried out upon reception.FIG. 9 shows the signal processing steps of channel decoding and errorcorrection carried out on the received signal, received by the readingmeans 70 for the reproducing arrangement of FIG. 7. The reproducingarrangement of FIG. 9 therefore comprise a channel decoder 80, wellknown in the art, and an error correction unit 82, also well known inthe art, so as to obtain a replica of the original audio signal.

Whilst the invention has been described with reference to preferredembodiments thereof, it is to be understood that these are notlimitative examples. Thus, various modifications may become apparent tothose skilled in the art, without departing from the scope of theinvention, as defined by the claims.

Further, the invention lies in each and every novel feature orcombination of features.

I claim:
 1. A data compression apparatus for data compressing a digitalinformation signal obtained from a digital audio signal, the digitalinformation signal comprising p-bit samples, where p is an integerlarger than 1, the apparatus comprising:means for receiving the digitalinformation signal, lossless compression means for carrying out asubstantially lossless compression step on the digital informationsignal so as to obtain a data compressed digital information signal, thelossless compression means comprising a Huffman type encoder, outputmeans for supplying the data compressed digital information signal,characterized in - that the Huffman type encoder is a Rice encoder,which Rice encoder is distinguishable by a code parameter m, the Riceencoder comprising generator means for generating said code parameterfrom N samples of the digital information signal in accordance with thefollowing formula: ##EQU8## where A and B are constants and x[n] is then-th sample of the N samples, where N is an integer larger than
 0. 2.Apparatus as claimed in claim 1, wherein the generator means are adaptedto generate said code parameter for subsequent frames of N samples ofthe digital information signal, the generator means being adapted togenerate the code parameter for a frame in accordance with said formula,where x[n] is the n-th sample in said frame and where N is largerthan
 1. 3. Apparatus as claimed in claim 1, wherein m=.left brkt-bot.M,where ##EQU9## and the sign `.left brkt-bot.` signifies a rounding ofthe value of M to the value of the nearest lower integer.
 4. Apparatusas claimed in claim 1, wherein A=1 and B=1.
 5. Apparatus as claimed inclaim 1, further comprising prediction means having an input forreceiving the digital audio signal and signal combination means, theprediction means being adapted to receive the digital audio signal andto generate an output signal which is a predicted version of the digitalaudio signal, the signal combination means being adapted to combine theaudio signal and the predicted version of the audio signal in asubtractive way so as to obtain said digital information signal and tosupply the digital information signal to said terminal means. 6.Transmitter for transmitting a data compressed digital informationsignal via a transmission medium, wherein the transmitter comprises thedata compression apparatus as claimed in claim 1, the transmitterfurther comprising means for applying the data compressed digitalinformation signal to the transmission medium.
 7. Transmitter as claimedin claim 6, wherein the transmitter further comprises error correctionencoding means and/or channel encoding means, for error correctionencoding and/or channel encoding the data compressed digital informationsignal prior to applying the data compressed digital information signalto the transmission medium.
 8. Transmitter as claimed in claim 6, whichis in the form of a recording apparatus for recording the datacompressed digital information signal in a track on a record carrier,comprising writing means for writing the data compressed digitalinformation signal on the record carrier.
 9. A data expansion apparatusfor data expanding a data compressed digital information signal obtainedfrom a digital audio signal, the apparatus comprising:input means forreceiving the data compressed digital information signal, losslessexpanding means for carrying out a substantially lossless data expansionstep on the data compressed digital information signal so as to obtain areplica of the digital information signal, the lossless expanding meanscomprising a Huffman type decoder, output means for supplying thereplica of the digital information signal, characterized in that theHuffman type decoder is a Rice decoder, which Rice decoder isdistinguishable by a code parameter m, the Rice decoder comprisinggenerator means for generating said code parameter from N samples of thereplica of the digital information signal in accordance with thefollowing formula: ##EQU10## where A and B are constants and x[n] is then-th sample of the N samples, where N is an integer larger than
 0. 10.Apparatus as claimed in claim 9, wherein m =.left brkt-bot.M, where##EQU11## and the sign `.left brkt-bot.` signifies a rounding of thevalue of M to the value of the nearest lower integer.
 11. Apparatus asclaimed in claim 9, wherein A=1 and B=1.
 12. Receiver for receiving adata compressed digital information signal from a transmission medium,wherein the receiver comprises the data expansion apparatus as claimedin claim 9, the receiver further comprising means for retrieving thedata compressed digital information signal from the transmission medium.13. Receiver as claimed in claim 12, wherein the receiver furthercomprises channel decoding means and/or error correction means, forchannel decoding and/or error correcting the data compressed digitalinformation signal prior to data expanding the data compressed digitalinformation signal.
 14. Receiver as claimed in claim 12, which is in theform of a reproducing apparatus for reproducing the data compresseddigital information signal from a track on a record carrier, comprisingreading means for reading the data compressed digital information signalfrom the record carrier.
 15. A method for data compressing a digitalinformation signal obtained from a digital audio signal, the digitalinformation signal comprising p-bit samples, where p is an integerlarger than 1, the method comprising the steps of:receiving the digitalinformation signal, carrying out a substantially lossless compressionstep on the digital information signal so as to obtain a data compresseddigital information signal, the lossless compression means comprising aHuffman type encoding step, supplying the data compressed digitalinformation signal, characterized in that the Huffman type encoder stepis an encoding step using a Rice encoder, which Rice encoder isdistinguishable by a code parameter m, the Rice encoding step comprisingthe substep of generating said code parameter from N samples of thedigital information signal in accordance with the following formula:##EQU12## where A and B are constants and x[n] is the n-th sample of theN samples, where N is an integer larger than 0.